PHYSICAL REVIEW C VOLUME 57, NUMBER 4 APRIL 1998

Selected Abstracts from Physical Review D

Abstracts of papers published in Physical Review D which may be of interest to our readers are printed here.

Cosmic ray composition from multiple data with the 700 064, India; S. K. Samaddar, Saha Institute of , KGF underground detector. H. R. Adarkar, S. R. Dugad, M. R. 1/AF, Bidhan Nagar, Calcutta 700 064, India. ͑Received 18 De- Krishnaswamy, M. G. K. Menon, N. K. Mondal, V. S. Narasim- cember 1996; published 10 February 1998͒ ham, and B. V. Sreekantan, Tata Institute of Fundamental Re- search, Homi Bhabha Road, Bombay, India 400 005; Y. Hayashi, The possibility of the formation of a droplet phase ͑DP͒ inside a N. Ito, S. Kawakami, S. Miyake, and Y. Uchihori, Osaka City Uni- star and its consequences on the structural properties of the star are versity, Osaka 558, Japan. ͑Received 27 August 1997; published 6 investigated. For nuclear , an equation of state ͑EOS͒ based February 1998͒ on a finite-range, momentum- and density-dependent ͑FRMDD͒ in- teraction, which predicts that matter undergoes a ferromag- The Kolar Gold Field ͑KGF͒ experiment was operated for about 6 netic transition at densities realizable inside the , is years at a depth of about 6045 hg/cm 2 using a calorimetric, fine- employed. An EOS for matter with density-dependent quark grain detector and recorded 307 multiple muon events in addition to masses, the so-called effective mass model, is constructed by cor- about 23000 single . The mean sea level energy of muons rectly treating the quark chemical potentials. A comparative study arriving vertically at this depth being around 7 TeV, one has a of hybrid star properties as obtained within the usual bag model and sensitive probe for the chemical composition of primary cosmic the effective mass model shows that both these models yield similar rays at energies around the knee in the energy spectrum. Predictions results. Then the effect of spin polarization on the formation of the based on several rigidity dependent composition models are com- DP is investigated. Using the EOS based on the FRMDD interac- pared with observed multiplicity spectrum. The data strongly sup- tion along with the usual bag model, it is also found that a droplet port a mixed chemical composition with medium to heavy prima- phase consisting of matter and unpolarized nuclear ries contributing substantially beyond 1015 eV. The proposed model matter sandwiched between a core of polarized nuclear matter and a explains all the features of the data and is consistent with the results crust containing unpolarized nuclear matter exists. Moreover, one from direct measurements as well as the all energy spec- could, in principle, explain the mass and surface magnetic field trum. ͓S0556-2821͑98͒00207-0͔͓Phys. Rev. D 57, 2653 ͑1998͔͒ satisfactorily and also allow, due to the presence of a droplet phase, the direct URCA process to happen. ͓S0556-2821͑98͒04804-8͔ ͓Phys. Rev. D 57, 3242 ͑1998͔͒

Hadronic couplings via QCD sum rules using three-point func- tions: Vacuum susceptibilities. Mikkel B. Johnson, Los Alamos Nonequilibrium evolution of a ‘‘tsunami,’’ a high multiplicity National Laboratory, Los Alamos, New Mexico 87545; Leonard S. initial quantum state: Dynamical symmetry breaking. Daniel Kisslinger, Department of Physics, Carnegie Mellon University, Boyanovsky,1 Hector J. de Vega,2 Richard Holman,3 S. Prem Pittsburgh, Pennsylvania 15213. ͑Received 8 July 1996; pub- Kumar,3 and Robert D. Pisarski,41Department of Physics and As- lished 2 February 1998͒ tronomy, University of Pittsburgh, Pittsburgh, Pennsylvania 15260 2LPTHE, Universite´ Pierre et Marie Curie (Paris VI) et Denis Di- We develop a three-point formalism to treat vacuum susceptibili- derot (Paris VII), Tour 16, 1 er. e´tage, 4, Place Jussieu 75252 ties used for the coupling of currents to within the method Paris, Cedex 05, France 3Department of Physics, Carnegie Mellon of QCD sum rules. By introducing nonlocal condensates, with the University, Pittsburgh, Pennsylvania 15213 4Department of Phys- space-time structure taken from fits to experimental parton distrbu- ics, Brookhaven National Laboratory, Upton, New York 11973. tions, we show that one can treat hadronic coupling at zero or low ͑Received 7 November 1997; published 4 February 1998͒ momentum transfer as well as medium and asymptotic momentum transfers and obtain a general expression for the vacuum suscepti- We propose to study the nonequilibrium features of heavy-ion bilities of the two-point formalism. The susceptibility, for collisions by following the evolution of an initial state with a large which there has been a major uncertainty, is evaluated successfully number of quanta with a distribution around a momentum ͉kជ 0͉ cor- with no new parameters. ͓S0556-2821͑98͒00107-6͔͓Phys. Rev. D responding to a thin spherical shell in momentum space, a ‘‘tsu- 57, 2847 ͑1998͔͒ nami.’’ An O(N)(⌽ជ 2)2 model field theory in the large N limit is used as a framework to study the nonperturbative aspects of the nonequilibrium dynamics including a resummation of the effects of the medium ͑the initial particle distribution͒. In a theory where the symmetry is spontaneously broken in the absence of the medium, Hybrid stars: Spin-polarized nuclear matter and density- when the initial number of per correlation volume is cho- dependent quark masses. V. S. Uma Maheswari, Variable Energy sen to be larger than a critical value the medium effects can restore Cyclotron Centre, 1/AF, Bidhan Nagar, Calcutta 700 064, India the symmetry of the initial state. We show that if one begins with and Institut fu¨r Theoretische Physik der Universita¨tTu¨bingen, Auf such a symmetry-restored, nonthermal, initial state, nonperturbative der Morgenstelle 14, D-72076 Tu¨bingen, Germany; J. N. De, Vari- effects automatically induce spinodal instabilities leading to a dy- able Energy Cyclotron Centre, 1/AF, Bidhan Nagar, Calcutta namical breaking of the symmetry. As a result there is explosive

57 2071 © 1998 The American Physical Society 2072 SELECTED ABSTRACTS 57 particle production and a redistribution of the particles towards low 305, Japan 5Institute of Particle and Nuclear Studies, High Energy momentum due to the nonlinearity of the dynamics. The asymptotic Accelerator Research Organization (KEK), Tsukuba, Ibaraki 305, behavior displays the onset of Bose condensation of and the Japan 6Faculty of Engineering, Yamanashi University, Kofu 400, equation of state at long times is that of an ultrarelativistic gas Japan. ͑Received 14 October 1997; published 9 March 1998͒ although the momentum distribution is nonthermal. ͓S0556-2821͑98͒05906-2͔͓Phys. Rev. D 57, 3653 ͑1998͔͒ We report on a study of the two-flavor finite-temperature chiral phase transition employing the Kogut-Susskind quark action and the plaquette action in lattice QCD for a lattice with Ntϭ4 temporal size. Hybrid R simulations of 104 trajectories are made at quark masses of mqϭ0.075,0.0375,0.02,0.01 in lattice units for the Ultrahigh energy - cross section and radiative spatial sizes 83,123, and 163. The spatial size dependence of various corrections. Gu¨nter Sigl, Department of Astronomy and Astrophys- susceptibilities confirm the previous conclusion of the absence of a ics, The University of Chicago, Chicago, Illinois 60637-1433. ͑Re- phase transition down to mqϭ0.02. At mqϭ0.01 an increase of 3 ceived 21 August 1997; published 4 February 1998͒ susceptibilities is observed up to the largest volume 16 explored in the present work. We argue, however, that this increase is likely to Several proposals exist to detect cosmic of energy from be due to an artifact of too small a lattice size and it cannot be taken tens of GeV up to the highest energies observed for cosmic rays, to be the evidence for a first-order transition. Analysis of critical ϳ1020 eV, or possibly even beyond. Detection efficiencies depend exponents estimated from the quark mass dependence of suscepti- crucially on the neutrino-nucleon cross section at these energies at bilities shows that they satisfy hyperscaling consistent with a which radiative corrections beyond the lowest order approximation second-order transition located at mqϭ0. The exponents obtained could become non-negligible. The differential cross sections can be from larger lattice, however, deviate significantly from both those modified by more than 50% in some regions of phase space. Esti- of O͑2͒, which is the exact symmetry group of the Kogut-Susskind mates of corrections to the quantities most relevant for neutrino action at finite lattice spacing, and those of O͑4͒ expected from an detection at these energies give, however, less dramatic effects: The effective ␴ model analysis in the continuum limit. ͓S0556-2821͑98͒04107-1͔͓Phys. Rev. D 57, 3910 ͑1998͔͒ average inelasticity in the outgoing is increased from Ӎ0.19 to Ӎ0.24. The inclusive cross section is reduced by roughly half a percent. The dominant uncertainty of the ultrahigh energy neutrino-nucleon cross section therefore still comes from uncertainties of the parton distributions in the nucleon at very low CPT and Lorentz tests in Penning traps. Robert Bluhm, Physics momentum fractions. ͓S0556-2821͑98͒01906-7͔͓Phys. Rev. D 57, Department, Colby College, Waterville, Maine 04901; V. Alan Ko- 3786 ͑1998͔͒ stelecky´ and Neil Russell, Physics Department, Indiana University, Bloomington, Indiana 47405. ͑Received 30 October 1997; pub- lished 19 February 1998͒

A theoretical analysis is performed of Penning-trap experiments Energy and zenith angle distribution of upward going muons testing CPT and Lorentz symmetry through measurements of and neutrino oscillations. Paolo Lipari and Maurizio Lusignoli, anomalous magnetic moments and charge-to-mass ratios. Possible Dipartimento di Fisica, Universita` di Roma ‘‘la Sapienza’’ and CPT and Lorentz violations arising from spontaneous symmetry I.N.F.N., Sezione di Roma, Piazzale A. Moro 2, I-00185 Roma, breaking at a fundamental level are treated in the context of a gen- Italy. ͑Received 10 December 1997; published 11 March 1998͒ eral extension of the SU͑3͒ϫSU͑2͒ϫU͑1͒ standard model and its restriction to quantum electrodynamics. We describe signals that The energy and zenith angle distribution of neutrino induced, might appear in principle, introduce suitable figures of merit, and upward going muons can give direct information on the presence of estimate CPT and Lorentz bounds attainable in present and future ␯ oscillations in precisely the range of parameters suggested as a Penning-trap experiments. Experiments measuring anomaly fre- solution of the atmospheric neutrino problem. We show that the quencies are found to provide the sharpest tests of CPT symmetry. Ϫ20 shape of the zenith angle distribution of the muon flux is quite Bounds are attainable of approximately 10 in the - Ϫ23 insensitive to modifications of the theoretical input and is therefore case and of 10 for a suggested experiment with an excellent probe for neutrino oscillations. We conclude that the and . Searches for diurnal frequency variations in these existing data sample on ␯-induced muons has the statistical power experiments could also limit certain types of Lorentz violation to Ϫ18 to confirm or refute the ␯-oscillation solution of the atmospheric the level of 10 in the electron-positron system and others at the Ϫ21 neutrino problem. ͓S0556-2821͑98͒50807-7͔͓Phys. Rev. D 57, level of 10 in the - system. In contrast, mea- 3842 ͑1998͔͒ surements comparing cyclotron frequencies are sensitive within the present theoretical framework to different kinds of Lorentz viola- tion that preserve CPT. Constraints could be obtained on one figure of merit in the electron-positron system at the level of 10Ϫ16,on another in the proton-antiproton system at 10Ϫ24, and on a third at Scaling study of the two-flavor chiral phase transition with the 10Ϫ25 using comparisons of HϪ ions with antiprotons. 1 Kogut-Susskind quark action in lattice QCD. S. Aoki, M. ͓S0556-2821͑98͒04207-6͔͓Phys. Rev. D 57, 3932 ͑1998͔͒ Fukugita,2 S. Hashimoto,3 N. Ishizuka,1,4 Y. Iwasaki,1,4 K. Kanaya,1,4 Y. Kuramashi,5 H. Mino6, M. Okawa,5 A. Ukawa,1 and T. Yoshie´1,4 ͑JLQCD Collaboration͒ 1Institute of Physics, Univer- sity of Tsukuba, Tsukuba, Ibaraki 305, Japan 2Institute for Cosmic Instantons and the chiral phase transition at nonzero Ray Research, University of Tokyo, Tanashi, Tokyo 188, Japan density. T. Scha¨fer, Institute for Nuclear Theory, Department of 3Computing Research Center, High Energy Accelerator Research Physics, University of Washington, Seattle, Washington 98195. ͑Re- Organization (KEK), Tsukuba, Ibaraki 305, Japan 4Center for ceived 11 August 1997; revised manuscript received 18 November Computational Physics, University of Tsukuba, Tsukuba, Ibaraki 1997; published 27 February 1998͒ 57 SELECTED ABSTRACTS 2073

We study an interacting ensemble of instantons at a finite baryon relations to the correlation function analysis are discussed. chemical potential. We emphasize the importance of fermionic zero ͓S0556-2821͑98͒01907-9͔͓Phys. Rev. D 57, 4124 ͑1998͔͒ modes and calculate the induced interaction between in- stantons at a nonzero chemical potential. We show that unquenched simulations of the instanton ensemble are feasible in two regimes, for a sufficiently small and for a very large chemical potential. At a very large chemical potential chiral symmetry is restored and the instanton ensemble is dominated by strongly correlated chainlike Study of the resummation of chiral logarithms in the exponen- configurations. ͓S0556-2821͑98͒03407-9͔͓Phys. Rev. D 57, 3950 tiated expression for the pion form factor. Francisco Guerrero, ͑1998͔͒ Departament de Fı´sica Teo`rica, Universitat de Vale`ncia and IFIC, CSIC–Universitat de Vale`ncia, C/ del Dr. Moliner 50, E-46100 Burjassot (Vale`ncia), Spain. ͑Received 20 November 1997; pub- lished 27 February 1998͒

From the properties of analyticity and unitarity an exponentiated Implications of 4 texture zeros mass matrices for neutrino expression for the pion form factor has been recently obtained. In anomalies. P. S. Gill and Manmohan Gupta, Centre of Advanced this work I show the validity of this expression comparing its order Study, Department of Physics, Panjab University, Chandigarh- p6 term with the one exactly calculated in ChPT. 160014, India. ͑Received 2 May 1997; revised manuscript received ͓S0556-2821͑98͒04307-0͔͓Phys. Rev. D 57, 4136 ͑1998͔͒ 14 October 1997; published 19 February 1998͒

Phenomenological 4 texture zeros mass matrices, successful in accommodating the CKM phenomenology, are used to simulta- neously explain the three neutrino anomalies: the solar neutrino Charmlets. Ju¨rgen Schaffner-Bielich, Nuclear Science Division, problem ͑SNP͒, the atmospheric neutrino problem ͑ANP͒, and the Lawrence Berkeley National Laboratory, University of California, LSND anomaly. When the SNP is resolved through vacuum oscil- Berkeley, California 94720; Axel P. Vischer, The Niels Bohr Insti- lations, we obtain a solution implying large mixing. In case the SNP tute, Blegdamsvej 17, DK-2100 Copenhagen O” , Denmark. ͑Re- is resolved through the MSW mechanism, the neutrino masses fol- ceived 29 October 1997; published 27 February 1998͒ low a ‘‘natural’’ hierarchy. ͓S0556-2821͑98͒01007-8͔͓Phys. Rev. D 57, 3971 ͑1998͔͒ We discuss the possibility that multiply charmed exotics are pro- duced in ultrarelativistic heavy ion collisions. Production probabili- ties at BNL RHIC are estimated and found to be large enough to allow for the possible detection of single and double charmed ex- otics. We demonstrate that charm matter is bound due to an attrac- tive one-gluon exchange potential. Furthermore, we study the color Two loops calculation in chiral perturbation theory and the uni- magnetic and color electric potential separately, as well as the tarization program of current algebra. J. Sa´ Borges, J. Soares group structure of such exotics, and estimate their masses. Barbosa, and M. D. Tonasse, Instituto de Fı´sica, Universidade do ͓S0556-2821͑98͒04807-3͔͓Phys. Rev. D 57, 4142 ͑1998͔͒ Estado do Rio de Janeiro, Rua Sa˜o Francisco Xavier 524, 20550- 013–Rio de Janeiro, RJ Brazil. ͑Received 29 August 1997; pub- lished 18 February 1998͒

In this paper we compare the two loop chiral perturbation theory calculation of pion-pion scattering with the unitarity second-order correction to the current algebra soft-pion theorem. It is shown that Physics beyond the standard model with a new reactor experi- both methods lead to the same analytic structure for the scattering ment. M. Moretti, Department of Physics, Ferrara University and amplitude. ͓S0556-2821͑98͒06105-0͔͓Phys. Rev. D 57, 4108 INFN sez. di Ferrara, via Paradiso 6, I44100 Ferrara, Italy; C. ͑1998͔͒ Broggini, Department of Physics, Padova University and INFN sez. di Padova, via Marzolo 8, 35131 Padova, Italy; G. Fiorentini, De- partment of Physics, Ferrara University and INFN sez. di Ferrara, via Paradiso 6, I44100 Ferrara, Italy. ͑Received 23 May 1997; published 2 March 1998͒ ؊ 1 Decays of 2 in chiral effective theory. Y. Nemoto, D. Jido, and M. Oka, Department of Physics, Tokyo Institute of Tech- We discuss the sensitivity to new physics of a measurement of ¯ Ϫ ¯ Ϫ nology, Meguro, Tokyo 152, Japan; A. Hosaka, Numazu College of the ␯ee ␯ee cross section at a nuclear reactor, with an accuracy Technology, 3600 Ooka, Numazu 410, Japan. ͑Received 22 October as that foreseen→ for the MUNU experiment. In particular we con- 1997; published 20 February 1998͒ ¯ Ϫ sider the anomalous contribution to ␯ee scattering arising from extra doublet scalars fields, additional Z , and more exotic We construct an SU(3) ϫSU(3) symmetric chiral effective L R particles, such as leptonic . ͓S0556-2821͑98͒03603-0͔ model which includes parity pair baryon fields. It is assumed that ͓Phys. Rev. D 57, 4160 ͑1998͔͒ the positive and negative parity baryons in the parity pair have opposite chiral transformation properties than each other. Using this model, strong decays of the negative parity baryons are studied up to the order of one-loop corrections. The results agree qualitatively with experiment in the ␲ and K channels. We examine how the Inelastic photoproduction of polarized J/␺. M. Beneke, Theory model parameters are determined from the decay widths and study Division, CERN, CH-1211 Geneva 23, Switzerland M. Kra¨mer, Ru- their physical meaning. The possibilities to build other models and therford Appleton Laboratory, Chilton, Didcot, OX11 0QX, En- 2074 SELECTED ABSTRACTS 57 gland; M. Va¨nttinen, NORDITA, Blegdamsvej 17, DK- It is shown that the short-range part of the Goldstone ex- 2100 Copenhagen O” , Denmark. ͑Received 17 September 1997; change interaction between the constituent , which explains published 27 February 1998͒ baryon spectroscopy and the short-range repulsion in the NN sys- tem, induces a strong short-range repulsion in the flavor-singlet We study the polar and azimuthal decay angular distribution of state of the SϭϪ2 system with J Pϭ0ϩ. This suggests that a J/␺ in photoproduction experiments as functions of the deeply bound H-particle should not exist. We compare our ap- inelasticity variable z and transverse momentum p . Future mea- t proach with other models employing different hyperfine interac- surements of decay angular distributions at the DESY ep collider HERA will provide a new test of theoretical approaches to factor- tions between quarks in the nonperturbative regime of QCD. ization between perturbation theory and bound-state ͓S0556-2821͑98͒04007-7͔͓Phys. Rev. D 57, 4393 ͑1998͔͒ dynamics and shed light on the color-octet production fraction in various regions of z and pt . ͓S0556-2821͑98͒03705-9͔͓Phys. Rev. D 57, 4258 ͑1998͔͒

CP violation versus the matter effect in long-baseline neutrino oscillation experiments. Hisakazu Minakata, Department of Phys- Off-forward quark distributions of the nucleon in the large-Nc limit. V. Yu. Petrov, P. V. Pobylitsa, and M. V. Polyakov, Peters- ics, Tokyo Metropolitan University, Minami-Osawa, Hachioji, ´ burg Nuclear Physics Institute, Gatchina, St. Petersburg 188350, Tokyo 192-03, Japan; Hiroshi Nunokawa, Instituto de Fısica Cor- Russia; I. Bo¨rnig, K. Goeke, and C. Weiss, Institut fu¨r Theoretische puscular, C.S.I.C., Department of Fı´sica Teo`rica, Universitat de Physik II, Ruhr-Universita¨t Bochum, D-44780 Bochum, Germany. Vale´ncia, 46100 Burjassot, Valencia, Spain. ͑Received 30 April ͑Received 8 October 1997; published 19 February 1998͒ 1997; published 6 March 1998͒

We study the off-forward quark distributions ͑OFQD’s͒ in the We investigate, within the framework of three generations of neu- chiral quark-soliton model of the nucleon. This model is based on trinos, the effects of CP violation in long-baseline neutrino oscil- the large-Nc picture of the nucleon as a soliton of the effective lation experiments. We aim at illuminating the global feature of the chiral Lagrangian and allows one to calculate the leading twist interplay between a genuine effect due to the CP-violating phase quark and antiquark distributions at a low normalization point. We and a fake one due to the Earth matter effect. To this goal, we demonstrate the consistency of the approach by checking various develop a formalism based on the adiabatic approximation and per- sum rules for the OFQD’s. We present numerical estimates of the turbative treatment of the matter effect which allows us to obtain isosinglet distribution H(x,␰,⌬2). In contrast with other approaches approximate analytic expressions of the oscillation probabilities. we find a strong qualitative dependence on the longitudinal momen- We present an order-of-magnitude estimation and a detailed nu- 2 tum transfer, ␰. In particular, H(x,␰,⌬ ) as a function of x exhibits merical computation of the absolute and the relative magnitudes of fast crossovers at ͉x͉ϭ␰/2. Such behavior could lead to a consider- the CP violations under the mass hierarchy suggested by the atmo- able enhancement of the deeply virtual Compton scattering cross spheric neutrino anomaly and the cosmological . We section. ͓S0556-2821͑98͒00807-8͔͓Phys. Rev. D 57, 4325 ͑1998͔͒ find that the genuine CP-violating effect is at most ϳ1%, and the matter effect dominates over the intrinsic CP violation only in a region of parameters where the oscillation probability of ␯ ␯ is ␮→ e large. ͓S0556-2821͑98͒06305-X͔͓Phys. Rev. D 57, 4403 ͑1998͔͒ Accelerator measurements needed to resolve uncertainties in primary cosmic ray composition and inelasticity. C. G. S. Costa, Department of Physics, University of Wisconsin, Madison, Wiscon- sin 53706. Received 21 July 1997; published 27 February 1998 ͑ ͒ Space-time description of neutrino flavor oscillations. Yu. V. We discuss an intrinsic ambiguity on the interpretation of results Shtanov, Inter-University Centre for Astronomy and Astrophysics, on cosmic-ray physics, related to the impossibility of deducing two Post Bag 4, Ganeshkhind, Pune 411 007, India and Bogolyubov unknowns: the chemical composition of primary cosmic rays and Institute for Theoretical Physics, Kiev 252143, Ukraine. ͑Received the dynamics of particle interactions in the fragmentation region, 17 June 1997; revised manuscript received 20 November 1997; based only on a single measurement. We indicate how measure- published 3 March 1998͒ ments of particle production at and near zero degrees—at extreme Recently the issue of EPR-like correlations in the mutual prob- values of rapidity or pseudorapidity —can overcome these uncer- ͑ ͒ ability of detecting a neutrino together with an accompanying tainties. Experiments of this nature are possible at the Fermilab charged lepton has received a new impetus. In this paper we de- Tevatron and will be possible at the CERN Large Collider, scribe this effect using the propagators of the particles involved in and should resolve the questions concerning the interpretation of Schwinger’s parametric integral representation. We find this de- cosmic ray data up to the highest measured energies. scription more simple and more suitable to the purpose than the S0556-2821 98 04507-X Phys. Rev. D 57, 4361 1998 ͓ ͑ ͒ ͔͓ ͑ ͔͒ usual momentum-space analysis. We consider the cases of a mono- chromatic neutrino source, wave packet source, and neutrino cre- ation in a localized space-time region. In the latter case we note that the space-time oscillation amplitude depends on the values of the How the ‘‘H particle’’ unravels the quark dynamics. Fl. Stancu neutrino masses, and becomes rather small for large relative mass and S. Pepin, Universite´ de Lie`ge, Institut de Physique B.5, Sart differences ͑mass hierarchy͒. We obtain the expressions for the os- Tilman, B-4000 Lie`ge 1, Belgium; L. Ya. Glozman, Institute for cillation and coherence lengths in various circumstances. In the Theoretical Physics, University of Graz, 8010 Graz, Austria. ͑Re- region of overlap our results confirm those of Dolgov et al. ceived 28 October 1997; published 2 March 1998͒ ͓S0556-2821͑98͒03307-4͔͓Phys. Rev. D 57, 4418 ͑1998͔͒ 57 SELECTED ABSTRACTS 2075

Atmospheric neutrino oscillation and a phenomenological lep- find these systems to be highly unstable against strong decays and ton mass matrix. M. Fukugita, Institute for Cosmic Ray Research, give a comparison with some of the previous literature. University of Tokyo, Tanashi, Tokyo 188, Japan and Institute for ͓S0556-2821͑98͒02207-3͔͓Phys. Rev. D 57, 4475 ͑1998͔͒ Advanced Study, Princeton, New Jersey 08540; M. Tanimoto, Fac- ulty of Education, Ehime University, Matsuyama 790-77, Japan T. Yanagida, Department of Physics, University of Tokyo, Tokyo 113, Japan. ͑Received 18 September 1997; published 27 February 1998͒ Spin content of ⌳ and its longitudinal polarization in e؉e؊ annihilation at high energies. C. Boros, Institut fu¨r Theoretische We propose simple phenomenological lepton mass matrices Physik, Freie Universita¨t Berlin, Arnimallee 14, 14195 Berlin, Ger- which describe the three neutrinos almost degenerate in mass, lead- many and Special Research Centre for the Subatomic Structure of Matter, University of Adelaide, Adelaide, Australia 5005; Liang ing to a very large mixing angle between ␯␮ and ␯␶ , as consistent with a recent report on atmospheric neutrino oscillations from the Zuo-tang, Institut fu¨r Theoretische Physik, Freie Universita¨t Berlin, SuperKamiokande Collaboration. Our matrix model also gives Arnimallee 14, 14195 Berlin, Germany and Department of Physics, Shandong University, Jinan, Shandong 250100, China. Received 8 ␯ Ϫ␯ mixing in agreement with the value required for neutrino ͑ e ␮ August 1997; published 18 February 1998͒ oscillation to explain the solar neutrino problem. ͓S0556-2821͑98͒03707-2͔͓Phys. Rev. D 57, 4429 ͑1998͔͒ Longitudinal polarization of ⌳ produced in eϩeϪ annihilation at CERN LEP energies is calculated in a picture for the spin content of ⌳ which is consistent with the polarized deep inelastic lepton- nucleon scattering data and SU͑3͒ flavor symmetry for Heavy hexaquarks in a chiral constituent . S. Pepin decay, so that the spin of ⌳ is not completely carried by its and Fl. Stancu, Universite´ de Lie`ge, Institut de Physique B.5, Sart s-valence quark. A comparison with the recent ALEPH data and the Tilman, B-4000 Lie`ge 1, Belgium. ͑Received 29 October 1997; pub- results of earlier calculations based on the static quark model, in which the spin of ⌳ is completely determined by the s quark, is lished 19 February 1998͒ given. The result shows that further measurements of such polariza- tion should provide useful information as to the question of which We discuss the stability of hexaquark systems of type uuddsQ picture is more suitable in describing spin effects in the fragmenta- ͑Qϭcorb͒within a chiral constituent quark model which success- tion processes. ͓S0556-2821͑98͒06205-5͔͓Phys. Rev. D 57, 4491 fully describes the baryon spectra including the charmed ones. We ͑1998͔͒